Broaching tool



Feb. l2, 1946. s. J`. SNOREK 2,394,723

BROACHING TOOL l Filed April 14, 1942 /N VE N TOE rme/vn' S. J SNG/enc Patented Feb. 12, 1946 BROACHING TOOL Stanley J. Snorek, Berwyn,

Ill., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application April 14, 1942, Serial No. 438,906

2 Claims.

This invention relates to a broaching tool for formin magnetic assemblies in electrical apparatus.

In the manufacture of some articles, for example, the magnet structure of electrical meas uring instruments, a high degree of precision is required, and, accordingly, difiiculties are encountered in forming cooperating surfaces of the magnet structure which define the air gap of the completed instrument. For example, in magnet structures where an annular core member is supported on the arcuate face of a pole shoe and is substantially surrounded by another pole piece with a c-shaped or open annular portion, it is particularly difiicult to so form and assemble the various parts that the air gap between the open annular or c-shaped pole shoe and the core member may be held within a few thousandths of an inch of one another uniformly throughout the entire effective area of the -pole piece having the open annular portion.

It is an object of the present invention to provide a broaching tool for forming articles With a high degree of precision.

In accordance With one embodiment of the invention, a bar of soft iron, which is to form the two pole pieces of the magnet structure, is milled to provide correspondingly shaped notches at opposed side faces thereof and after being so machined, the block `of metal has a pair of cshaped permanent magnets welded to it in the position which they are' to occupy in the meter for which the magnet assembly is designed. After the assembly of the magnets and the bar are thus attached together, 'a hole is drilled at approximately the center of the bar, thus leaving very small Sections of metal between the drilled hole and the slots formed on opposed surfaces of the bar. After the assembly is thus far machined, a round breach whose largest teeth are approximately ten thousandths of an inch larger than the drilled hole is drawn 'through the drilled hole to cut away the remaining thin portion ofthe metal between the slots and the drilled hole. This broaching operation is then followed by a broaching operation which leaves the relativelythin portion of the block, which is left, untouched by the teeth of the breach and a relatively larger hole is formed in the portion of the block which will ultimately form the open annular, c-shaped pole piece. The final step in forming the assembly comprises, in a single stroke of a broaching tool, cutting both of the pole pieces to their final contour and in order to do this, a novel type of broaching tool is utilized which comprises a guiding section of the same contour as the face of the pole piece which is to support the core on one side of the tool and teeth formed to cut the open annular or c-shaped pole piece to its final configuration on the other side thereof. The rear end of the special breaching tool is provided with a toothed portion diametrically opposed to a guiding portion, the toothed portion engaging and finishing the core supporting pole piece's core engaging face while a guiding surface bears on and is guided by the c-shaped or open annular pole piece. The tool for effecting this final broaching step comprises a relatively long rod of tool steel in which a slot has been milled for receiving a broachinginsert. Broach teeth are cut on the outer surface of the rod of tool steel to cut the open annular or c-shaped pole piece and the insert is provided with teeth for making the final cut on the core engaging surface of the core supporting pole piece,

A better understanding of the invention may be had by reference to the followingdetailed description when considered in conjunction with the 'accompanying drawing, wherein Fig.. 1 is an elevational view of a broaching tool for performin the final broaching step described hereinbefore;

Fig. 2 is a longitudinal sectional 'View taken along the line 2-2 of Fig. l in the direction of the arrows showing the broaching tool in cross section and on an enlarged scale, part of the tool -being broken away to permit showing it on a sufliciently large scale to clearly 'illustrate the construction of the tool;

Fig. 3 is a transverse sectional view taken through the broaching tool along the line 3-3 of Fig. 1 in the direction of the arrows and showing, in dotted lines, the relative position of the pole pieces;

Fig. 4 is a view similar to Fig. 3, but taken along the line 4-4 of Fig. 1 and showing the rear portion of the broaching tool in section, and

ing tool designated generally by the numeral '0,

comprises a shaft portion H having a notch '2 cut therein for attaching the broaching tool to any suitable broach operating mechanism. Intermediate its ends, the broaching tool Il' is enl larged te provide enlarged portion I 3, which has,

point designated '6 to the rear end of the enlarged portion '3, there is provided guiding surface !1 of the same diameter as the final teeth of the teeth '4. The portion '3 of the teel has a` shank '8 either formed integrally therewith or* suitably attached thereto and of a reduced diameter extending from it te facilitate handling the tool. The portion '3 of the tool has a longitudinal slet [3 milled throughout-its length in whicha toothed bar 20 may be secured by rivets 2l 2l. The portion of the bar 20 extending between the points l 5 and '5 is rounded, as shown ait-22 (Fig. 3) to serve as a guiding, surface and the portion of the tool extending from the point Hi toward the rear (the lower part Figs. I and 2) of the teel has teeth 23 cut in tr It should be noted that, as most clearly shown in Figs. '2, 3 and 4, the guide surface 22 and the cutting edges of the teeth 23' -are positioned inwardly from the teeth '4 and the guiding surface |`T, respectively.

The tool just described is utilized in the final step of the method of forming the magnet structure shown in Fig. 5. comprises, as finished, a pair of permanent mag attached at theiropposite ends, for example, by

, fore, the broaching tool IO is provided with teeth '4 gradually increasing in diameter from the point "5 to the point '6 (Fig. 1 and the surface at. 22 is of such configuration as te engage the eXtendi-ng end of the pole piece 32 during This magnet structure Welding, to pole pieces 32 and 33, the attachment being made along the line of' iuncture between the pole pieces and the magnets 30 and 3', as shewnat 34, 35, 36 and 31, respectvely. The pole piece 3 2 in the final construction is adapted to have an annular core member 38` fixed to it by means of the screw 39 extending through the pole piece, 32 and threadedly engaging threads cut in the side walls of a slet 40 formed in the annular core member 33. p r

The magniet structure thus briefly described is formed'by preliminarily milling a slot/4' on each side of a block of soft iron, which, prior to the milling eperation, was rectangular in shape. In performing this milling operation, the portions roughly indicated by the dotted lines 42 42' are cut from opposite sides `of the block of soft iron. After this operation is performed, the C-shaped permanent magnets 30 and 3' are welded to the block with the no tches cut in it and thereafter a hole, as indicated by'thedetted line the first portion of the stroke of the -tool '0. As soon as the portion of the broaching tool '0 between the points '5 and '6 has been drawn through the magnet structure, the teeth |4 will have out away/the metal between the dotted line 46 and a surface 48', thus ferming the face of the pole piece 33 to its ultimate configuration. Continued movement ofthe tool 'El will move the guiding surface l" V into engagement with the surface 48 of the pole piece s and' guide the' broaching tool IO while the teeth 23 cut the surface 50- of the pole piece 32 to its final shape.

It' will be understood that' the lines designated by the numerals 4l, 43, 45, 46 and 48 are only approximate indications of the location of these surfacesand that in actually performing these operations, the amount of metal removed in varieus' Strokes of the breaching tools are exceedingly small. As a matter of fact, in one magnet assembly made in accordance with this method, the drilled hele is' 464" in diameter; the first round breach is AM" in diameter; thesecond broachingtool, that is, the one with the fiat side on it, cuts slightly more than .0-10" from the pole piece 33; and the final 'breaching tool, that 43, is drilled in the block, thus leaving the upper end of the block attached te the lower end thereof only by the relatively small er thin Sections designated 44. After the hole has been drilled through the block, a circular breach, which will ream or enlarge the hele 43, is drawn through the hole 43, thereby to cut away the thin sections at 44 andenlarge the hole 43, to approximately the size indicated by the dotted line 45. After the hole in the block has been enlarged to the appreximate size, as shown by the dotted line 45, the block having been out into two sepai rate parts in this operation by cutting away the thin Sections at 44, a broachtool, conforming in cross section substantially to Circular configuraing 'the upper pole piece, which has now' been is, the tool Hl, cuts approximately .01(1"' from the surfaces 48 and 50. While these dimensions are given to illustrate the fineness with Which these various surfaces must: be. cut, the' dimensions themselves are 'net 'essential and other dimensions might' be used' depending uponthe dimensiens to which the structure is te. be cut; Furthermore, the recitation of these dimensions, 'while net an essential part of the invention, will illustrate the nicety with' which these surfaces must be formed' in order to provide ameter'magnet. structure which will operate with the desired 'accuracy when assembled" in a meter;

l. A hroaching, tool cemprising a forward portien having` teeth thereen extending throughout the greater part of a circle, an arcuately shaped guide portion having' the same axis as the teeth for guiding' the teeth, a rear portion having arouately shaped teeththereen coaxial with the teeth on the forward' portion, and a guide portion conforming to the largest teeth en the forward pertien.

2. A broaching tool comprising coaxial rear and forward cutting teeth for cutting different surfaces on a single streke of the tool and guiding portions dametrically opposed te said cutting teeth, ene guiding portion being positioned 

